1. Field of the Invention
The present invention relates to a terminal fitting and a mounting method, and more particularly to a terminal fitting that is mounted on the core wires made of aluminum or aluminum alloy and its mounting method.
2. Related Art
Various kinds of electronic devices are mounted on an automobile as a mobile unit. The automobile has arranged a wire harness for passing electric power through a wire from a battery etc. or a control signal from a control unit to the electronic devices. The wire harness comprises an electric wire and a connector. The connector comprises a housing formed of synthetic resin having insulating property and a terminal fitting accommodated within the housing and mounted at the terminal of the electric wire.
One example of the terminal fitting is shown in FIG. 10. FIG. 11 is a perspective view showing a state where the terminal fitting as shown in FIG. 10 is mounted on the electric wire. FIG. 12 is a cross-sectional view of FIG. 11, taken along the line III-III. The electric wire 10 comprises a plurality of core wires 11 and a sheath portion 12 for covering the core wires 11, as shown in FIG. 11. The terminal fitting 20 is obtained by bending a conductive sheet metal, and comprises an electric contact portion 21 for connecting the mating terminal fitting and a wire connection portion 22 for connecting the electric wire 10, as shown in FIG. 10.
The electric contact portion 21 comprises a rectangular barrel portion 23, and a spring piece, not shown, accommodated within the barrel portion 23. The barrel portion 23 is formed like a rectangular barrel in the shown example. The spring piece urges an inserter such as a male tab of the mating terminal fitting entered into the barrel portion 23 toward the inner surface of the barrel portion 23, and pinches the inserter with the inner surface. The electric contact portion 21 is connected with the mating terminal fitting electrically and mechanically, because the inserter such as the male tab of the mating terminal fitting is inserted into the barrel portion 23 and the spring piece pinches the inserter with the inner surface of the barrel portion 23.
The electrical connection portion 22 comprises a bottom wall 24 having an arcuate section, a pair of core wire caulking pieces 25, and a pair of sheath portion caulking pieces 26. The bottom wall 24 is continuous with an external wall of the barrel portion 23. The pair of core wire caulking pieces 25 and the pair of sheath portion caulking pieces 26 are stood from the bottom wall 24.
If the pair of core wire caulking pieces 25 are caulked in a state where the core wires 11 of the electric wire 10 are positioned on the bottom wall 24 between the pair of core wire caulking pieces 25, the core wires 11 of the electric wire 10 are crimped with the pair of core wire caulking pieces 25, as shown in FIG. 11. Also, if the pair of sheath portion caulking pieces 26 are caulked in a state where the core wires 12 of the electric wire 10 are positioned on the bottom wall 24 between the pair of sheath portion caulking pieces 26, the sheath portion 12 of the electric wire 10 is mounted on the pair of sheath portion caulking pieces 26, as shown in FIG. 11.
Copper or copper alloy that has excellent spring property and conductivity is typically used for the terminal fitting 20 having the spring piece, as described above. On the other hand, the copper wire that has excellent conductor property is typically used as the material of the core wires 11 of the electric wire 10.
By the way, the automobile as the mobile unit having the multi-function is asked by users. Therefore, the automobile tends to mount more electronic devices. Therefore, the electric wire 10 of the wire harness naturally increases, so that the mass and volume of the wire harness tend to increase.
Therefore, to reduce the size and weight of the wire harness, aluminum that has excellent conductor property and has one-third the specific weight of copper has begun to be used as the material of the core wires 11 of the electric wire 10. On the other hand, since the terminal fitting 20 has the spring piece as described above, there has been a demand for directly using the material of copper or copper alloy having excellent spring property.
However, copper or copper alloy has a greater spring back property than aluminum or aluminum alloy. Therefore, if the terminal fitting 20 made of copper or copper alloy is caulked to crimp the core wires 11 made of aluminum or aluminum alloy, the core wires are placed in a loose crimped state, whereby there was a problem that the contact resistance value at the crimped part increased to cause an imperfect contact. (See for example, JP-A-4-209471 and JP-A-56-48079.)